US20040090900A1 - Compatible optical pickup device using a single light source - Google Patents
Compatible optical pickup device using a single light source Download PDFInfo
- Publication number
- US20040090900A1 US20040090900A1 US09/899,501 US89950101A US2004090900A1 US 20040090900 A1 US20040090900 A1 US 20040090900A1 US 89950101 A US89950101 A US 89950101A US 2004090900 A1 US2004090900 A1 US 2004090900A1
- Authority
- US
- United States
- Prior art keywords
- optical disk
- light
- objective lens
- optical
- light source
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Images
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1372—Lenses
- G11B7/1374—Objective lenses
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
- G11B7/1367—Stepped phase plates
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
- G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
- G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD
Definitions
- the present invention relates to a compatible optical pickup device which can compatibly read/write optical disks of the CD family or DVD family, and more particularly, to a compatible optical pickup device using a single light source to emit light having a wavelength longer than 650 nm.
- a typical optical pickup device reproduces and records information on and/or from a recording medium in a non-contact manner.
- An optical pickup device capable of performing reproducing/recording of optical disks of the DVD family having a thickness of 0.6 mm (hereinafter referred to as “DVD”) uses an objective lens having a numerical aperture of 0.6 and a light source to emit light having a 650 nm wavelength.
- the optical pickup device for DVD should be compatible with optical disks of a CD family which is 1.2 mm thick (hereinafter referred to as “CD”).
- FIG. 1 A conventional optical pickup which can compatibly reproduce/record a CD and a DVD is shown in FIG. 1 and has the structure using two light sources 1 and 3 to emit light having different wavelengths.
- a first light source 1 emits light having 635 or 650 nm to reproduce/record a DVD 10 a , which is relatively thin.
- a second light source 3 emits light having a 780 nm wavelength to reproduce/record a CD 10 b , which is relatively thick.
- a grating 5 diffracts and splits light output from the second light source 3 into the 0 th order and the ⁇ 1 st order rays to detect a tracking error signal by a three-beam method during reproducing/recording of the CD 10 b .
- the light emitted from the first light source 1 passes through a first beam splitter 7 and is reflected by a second beam splitter 9 so as to proceed toward the DVD 10 a .
- the light emitted from the second light source 3 is sequentially reflected by the first and second beam splitters 7 and 9 and proceeds toward the CD 10 b .
- a collimating lens 11 converts the divergent light output from the first and second light sources 1 and 3 into a parallel beam.
- An objective lens 15 focuses incident light output from the first and second light sources 1 and 3 to form a light spot.
- the light emitted from the first light source 1 is focused on the relatively thin DVD 10 a while the light emitted from the second light source 3 is focused on the relatively thick CD 10 b.
- the light reflected by an optical disk 10 is incident on the second beam splitter via the objective lens 15 . Most of the light passes through the second beam splitter 9 and is received by a photodetector 19 after passing through a sending lens 17 to focus the incident light reflected by the optical disk 10 .
- the conventional compatible optical pickup device having the above structure includes two light sources 1 and 3 emitting light having different wavelengths, optical disks 10 of both the CD 10 b family and the DVD 10 a family can be reproduced/recorded.
- the conventional compatible optical pickup device uses two separate light sources, a cost of manufacturing is high and the structure thereof is complicated, and further, assembly and optical arrangement is difficult. Further, the light source 1 for a 635 nm or 650 nm wavelength which can emit recording power for DVD-R and/or DVD-RAM is expensive, which increases the entire cost of a compatible optical pickup device.
- an object of the present invention to provide an inexpensive compatible optical pickup device using a single light source to emit light having a wavelength longer than 650 nm so that an optical disk of the CD family and the DVD family can be compatibly reproduced/recorded.
- a compatible optical pickup device comprises a single light source to emit a light having a wavelength longer than 650 nm, an objective lens having a near axis area, a ring type annular lens area, and a far axis area with respect to an apex to focus the light emitted from the light source to form light spots suitable for a first optical disk which is relatively thin and a second optical disk which is relatively thick, so as to form a light spot having an FWHM (full width at half maximum) of 0.72 ⁇ m or less with respect to the first optical disk and a light spot having an FWHM greater than or equal to 0.8 ⁇ m with respect to the second optical disk, an optical path changer arranged on the optical path between the light source and the objective lens to change a path of incident light, and a photodetector to receive light reflected by the optical disk passed through the objective lens and the optical path changer and to detect an information signal and
- FWHM full width at half maximum
- a compatible optical pickup device comprises a single light source to emit a light having a wavelength longer than 650 nm, an objective lens having a near axis area, a ring type annular lens area, and a far axis area with respect to an apex to focus light emitted from the light source to form light spots suitable for a first optical disk which is relatively thin and a second optical disk which is relatively thick, and having an effective numerical aperture greater than or equal to 0.63 with respect to the first optical disk and an effective numerical aperture less than or equal to 0.53 with respect to the second optical disk, an optical path changer arranged on the optical path between the light source and the objective lens to change a path of the incident light, and a photodetector to receive the light reflected by the optical disk and passed through the objective lens and the optical path changer and to detect an information signal and/or error signal.
- the first optical disk is an optical disk of a DVD family and the second optical disk is an optical disk of a CD family.
- the light source emits light having a wavelength between 680-780 nm.
- the annular lens area of the objective lens is optimized to the second optical disk so that, when the first optical disk is to be reproduced/recorded, a light spot of light passing through the near axis area and the far axis area is focused on the information recording surface of the first optical disk, while, when the second optical disk is to be reproduced/recorded, a light spot of light passing through the near axis area and the annular lens area is focused on the information recording surface of the second optical disk.
- the optical path changer comprises a polarization hologram element to diffract incident light to the 0 th order ray, or +1 st order and/or ⁇ 1 st order rays according to a linear polarization component thereof, and a wave plate to change a polarization of the incident light.
- the optical path changer comprises a beam splitter arranged between the light source and the objective lens to transmit and/or reflect incident light.
- the beam splitter is provided to transmit or reflect incident light according to the polarization of the incident light, and a wave plate to change the polarization of the incident light is provided between the beam splitter and the objective lens.
- FIG. 1 schematically shows the optical arrangement of a conventional compatible optical pickup device
- FIG. 2 schematically shows the optical arrangement of a compatible optical pickup device using a single light source according to an embodiment of the present invention
- FIG. 3 is a graph schematically showing reflectance rates as a function of wavelength before and after recording of cyanine based CD-R and phthalo based CD-R, which are currently known;
- FIG. 4 is a graph schematically showing reflectance rates as a function of wavelength before and after recording of azo based DVD-R and cyanine based DVD-R, which are currently known;
- FIG. 5 is a plan view of the objective lens according to an embodiment of the present invention of FIG. 2;
- FIGS. 6A and 6B and 7 A and 7 B show the objective lens according to embodiments of the present invention for use in the compatible optical pickup of FIG. 2;
- FIG. 8 schematically shows the optical arrangement of a compatible optical pickup device using a single light source according to another embodiment of the present invention.
- FIG. 9 schematically shows the optical arrangement of a compatible optical pickup device using a single light source according to yet another embodiment of the present invention.
- FIGS. 10A and 10B are graphs indicating an aberration characteristic according to the field of an incident beam between the objective lens according to an embodiment of the present invention and the conventional 650 nm objective lens;
- FIGS. 11A and 11B are graphs indicating an aberration characteristic according to the tilt of an optical disk between the objective lens according to an embodiment of the present invention and the conventional 650 nm objective lens;
- FIG. 12 is a graph showing a reproduction signal value according to the depth of a pit when a DVD is reproduced by the compatible optical pickup device according to an embodiment of the present invention.
- a compatible optical pickup device includes a single light source 50 to emit a light having a wavelength longer than 650 nm, an objective lens 70 mounted and driven on an actuator (not shown) to focus and track so as to control the formation of a light spot suitable for each of the first and second optical disks 40 a and 40 b having different thicknesses by focusing the light output from the light source 50 , an optical path changer 60 disposed on an optical path between the light source 50 and the objective lens 70 to change a proceeding path of the incident light, and a photodetector 100 to receive the light reflected by an optical disk 40 .
- the first optical disk 40 a is an optical disk of the DVD family which is relatively thin
- the second optical disk 40 b is an optical disk of the CD family which is relatively thick.
- the light source 50 is a semiconductor laser that emits a light of a high optical power (i.e., an edge emitting laser or a vertical cavity surface emitting laser) to be used not only for reproducing information signals, but also for recording information signals.
- the light source 50 emits light having a wavelength longer than 650 nm, for example, a wavelength between 660 nm through 790 nm. As shown, the light source 50 emits light having a wavelength between 680 nm through 780 nm.
- the unit cost of production of a semiconductor laser for a wavelength longer than 650 nm is much lower than that of a semiconductor laser for a 650 nm wavelength.
- the unit cost of production of the light source 50 can be drastically reduced.
- the unit cost of production of the compatible optical pickup device according to the present invention can be drastically reduced.
- the cost of the compatible optical pickup device according to the present invention can be lowered, and simultaneously a CD-R which is currently commercialized can be compatibly reproduced/recorded.
- the currently commercialized CD-R has an organic pigment film recording layer having a large absorptivity with respect to light having a wavelength less than 750 nm, in order to reproduce/record the CD-R, a light source that emits a light having a wavelength equal to or greater than 750 nm is needed to prevent the destruction of recorded data due to a difference in sensitivity.
- the compatible optical pickup device can compatibly reproduce/record CD-Rs regardless of a wavelength range of the used light source 50 .
- a CD-R has a recording layer which is a organic pigment film having a large absorption rate with respect to light having a wavelength less than or equal to 750 nm
- a light source is needed that emits light having a wavelength greater than or equal to 750 nm to prevent damage to recorded data due to the difference of sensitivity.
- the light source 50 is a semiconductor laser that emits light having a wavelength less than or equal to 770 nm (preferably 760 ⁇ 10 nm)
- the compatible optical pickup device according to the present invention can be manufactured at a low cost and simultaneously be compatible with currently commercialized CD-Rs and DVD-Rs regardless of the type of organic pigment used therein.
- the currently commercialized CD-Rs and DVD-Rs are different in the absorption rate depending on the type of organic pigment film used therein. That is, as shown in FIG. 3, a cyanine-based CD-R and a phthalo-based CD-R, which are currently commercialized, are optimized to exhibit a large difference in the reflection rate before and after recording with respect to a wavelength of 780 nm. The difference in the reflection rate before and after recording according to the wavelength is characteristically different with respect to the organic pigment used therefor.
- the CD-R has a great absorption rate with respect to light having a wavelength less than or equal to 750 nm.
- a light source that emits light having a wavelength greater than or equal to 750 nm to prevent damage to recorded data due to the difference in sensitivity.
- an azo-based DVD-R and a cyanine-based DVD-R which are currently commercialized, are optimized to exhibit a large difference in the reflection rate before and after recording with respect to a wavelength of 650 nm.
- the difference in the reflection rate before and after recording according to the wavelength is characteristically different with respect to the organic pigment used therefor.
- the reflection rate is reversed in a wavelength area longer than about 770 nm. That is, the reflection rate before recording either becomes less than the reflection rate after recording, or the difference in the reflection rate before and after recording is approximately 0.
- a CD-R and a DVD-R can be compatibly used regardless of the type of organic pigment in use.
- the compatible optical pickup device when a CD-R is manufactured to have a less absorption rate with respect to light having a wavelength less than or equal to 750 nm, the compatible optical pickup device according to the present invention can compatibly use a CD-R regardless of the wavelength range of the light source 50 used. Also, for example, when an azo-based DVD-R is manufactured such that a reflection rate thereof is not reversed with respect to light having a wavelength greater than or equal to 770 nm, or the difference in the reflection rate before and after recording is great, the compatible optical pickup device according to the present invention can compatibly use a DVD-R regardless of the wavelength range of the light source in use.
- the optical path changer 60 comprises a holographic beam splitter having a polarization hologram element 61 to diffract incident light into a 0 th order ray, or a +1 st order and/or the ⁇ 1 st order rays according to a linear polarization component, and a wave plate 63 to convert the polarization of the incident light.
- a polarization hologram element 61 to diffract incident light into a 0 th order ray, or a +1 st order and/or the ⁇ 1 st order rays according to a linear polarization component
- a wave plate 63 to convert the polarization of the incident light.
- the polarization hologram element 61 is preferably arranged to diffract the light output from the light source 50 and linearly polarize the light in one direction into the 0 th order ray.
- the wave plate 63 is a quarter wave plate with respect to the wavelength of the light emitted from the light source 50 and is arranged to convert the linearly polarized light output from the light source 50 to a circularly polarized light.
- the light output from the light source 50 and linearly polarized light in one direction is diffracted into the 0 th order ray by the polarization hologram element 61 , converted to one circularly polarized light while passing through the wave plate 63 , and focused on the information recording surface of the optical disk 40 by the objective lens 70 .
- the focused light is reflected by the information recording surface of the optical disk 40 and converted to another circularly polarized light.
- the another circularly polarized light is converted to light linearly polarized in the other direction while passing through the wave plate 63 and diffracted into the +1 st order and/or ⁇ 1 st order rays by the polarization hologram element 61 , and proceeds toward the photodetector 100 .
- the photodetector 100 receives light reflected by the optical disk 40 and having passed through the objective lens 70 and the holographic beam splitter 60 , and detects an information signal and/or an error signal.
- the photodetector 100 includes a plurality of sectional plates (not shown), each of the sectional plates independently performing photoelectric conversion to detect the information signal and/or the error signal.
- the optical path changer 60 is the holographic beam splitter
- the photodetector 100 can be installed on a base 101 where the light source 50 is installed, the photodetector 100 and the light source 50 can be modularized.
- the holographic beam splitter 60 has a holographic device (not shown) by which most of the light output from the light source 50 is diffracted into the 0 th order ray, and most of the light reflected from the optical disk 40 is diffracted into the +1 st order ray and/or ⁇ 1 st order ray to be received by the photodetector 100 .
- the collimating lens 65 forms an indefinite optical system by changing the divergent light output from the light source 50 to a parallel light.
- the collimating lens 65 is preferably arranged between the optical path changer 60 and the objective lens 70 .
- the collimating lens 65 converts the divergent light output from the light source 50 to a parallel light and, simultaneously, the light reflected by the optical disk 40 and incident thereon to a focused light to proceed toward the photodetector 100 .
- the objective lens 70 has a near axis area 71 , a ring type annular lens area 73 , and a far axis area 75 with respect to an apex.
- the apex is a point at the intersection of the central axis of the objective lens 70 and the surface of the objective lens 70 .
- the annular lens area 73 is an area on which light of an intermediary area between the near axis area 71 and the far axis area 75 is incident, which is formed to be an oval ring or circular ring type on the surface of the objective lens 70 facing the light source 50 or the recording medium 40 .
- the annular lens area 73 is formed to be aspherical as shown in FIGS. 6A and 6B and is optimized with respect to the relatively thick second optical disk 40 b . If the annular lens area 71 has an aspherical shape optimized with respect to the second optical disk 40 b , when the relatively thin first optical disk 40 a is to be reproduced/recorded, the light emitted from the light source 50 passes through the near axis area 71 and the far axis area 75 and is thus focused on the information recording surface of the first optical disk 40 a . The light which passes through the annular lens area 73 between the near axis area 71 and the far axis area 75 is so spread that this light cannot reproduce/record information to/from the information recording surface of the first optical disk 40 a.
- the second optical disk 40 b When the second optical disk 40 b is used, of the light emitted from the light source 50 , the light passing through the near axis area 71 and the annular lens area 73 is focused on the information recording surface of the second optical disk 40 b as a light spot, while the light passing through the far axis area 75 is so spread so that it cannot be used to reproduce information from the information recording surface of the second optical disk 40 b.
- the annular lens area 73 can be formed to shield or scatter incident light.
- the first optical disk 40 a when the first optical disk 40 a is used, of the light emitted from the light source 50 , the light passing through the near axis area 71 and the far axis area 75 is focused on the information recording surface of the first optical disk 40 a as a light spot, while the light passing through the annular lens area 73 is shielded or scattered so that it cannot be focused on the information recording surface of the first optical disk 40 b .
- the second optical disk 40 b when the second optical disk 40 b is used, of the light emitted from the light source 50 , the light passing through the near axis area 71 is focused on the information recording surface of the second optical disk 40 b as a light spot. In contrast, the light passing the far axis area 75 is not focused on the information recording surface of the second optical disk 40 b with an intensity suitable for reproducing and/or recording, while the light passing through the annular lens area 73 is shielded or scattered so that it is not focused on the information recording surface of the second optical disk 40 b.
- the objective lens 70 having the structure according to the present invention is provided to focus the light output from the light source 50 so that a light spot suitable for each of the first and second optical disks 40 a and 40 b having different thicknesses can be formed. That is, the objective lens 70 according to the present invention preferably forms a light spot having an FWHM (full with at half maximum) equal to or less than 0.72 ⁇ m (a width which is equal to or less than 1.2 ⁇ m at 1/e 2 ) with respect to the first optical disk 40 a , and a light spot having an FWHM equal to or greater than 0.8 ⁇ m (a width which is equal to or greater than 1.3 ⁇ m at 1/e 2 ) with respect to the second optical disk 40 b.
- FWHM full with at half maximum
- the objective lens 70 has a numerical aperture related to the wavelength of the light emitted from the light source 50 . That is, when the light source 50 emits light having a wavelength between 680-780 nm, the objective lens 70 has an effective numerical aperture greater than or equal to 0.63 with respect to the first optical disk 40 a , and an effective numerical aperture less than or equal to 0.53 with respect to the second optical disk 40 b . When the light source 50 emits light having a 780 nm wavelength, the objective lens 70 preferably has an effective numerical aperture equal to or greater than 0.7 with respect to the first optical disk 40 a , and an effective numerical aperture less than or equal to 0.53 with respect to the second optical disk 40 b.
- the objective lens 70 when the light source 50 emits light having a wavelength of 680 nm, 720 nm, 760 nm, or 780 nm, the objective lens 70 has an effective numerical aperture of about 0.63, 0.66, 0.7, or 0.72 with respect to the first optical disk 40 a . Also, when the light source 50 emits light having a wavelength between 750-780 nm, the objective lens 70 preferably has an effective numerical aperture of 0.7 or more with respect to a DVD and 0.53 or less with respect to a CD. For example, when the light source 50 emits light having a wavelength of 760 ⁇ 10 nm, the objective lens 70 preferably has an effective numerical aperture of 0.7 with respect to a DVD and 0.53 with respect to a CD.
- FIG. 2 shows a case in which the objective lens 70 having the annular lens area 73 having an aspherical shape described with reference to FIG. 6A is used.
- the objective lens 70 is schematically illustrated to show the focus of the light according to the incident areas.
- the light incident surface of the second optical disk 40 b is disposed closer to the objective lens 70 than the light incident surface of the first optical disk 40 a . This is to show a difference in a distance between the objective lens 70 and the light incident surface of the first optical disk 40 a and a distance between the objective lens 70 and the light incident surface of the second optical disk 40 b (i.e., a working distance difference).
- the light incident surfaces of the first and second optical disks are located at the same position, and when the second optical disk 40 b is used, the objective lens 70 is driven by an actuator to be moved closer to the second optical disk 40 b than in the first optical disk 40 a to be suitable for the working distance.
- the compatible optical pickup device includes a beam splitter type optical path changer.
- the optical path changer is a polarizing beam splitter 161 disposed between the light source 50 and the objective lens 70 to transmit or reflect the incident light according to its polarization, and a wave plate 163 disposed between the polarizing beam splitter 161 and the objective lens 70 to convert the polarization of an incident light.
- the optical path changer is a beam splitter 260 disposed between the light source 50 and the objective lens 70 to transmit and reflect the incident light in a predetermined ratio.
- a sensing lens 167 is disposed on the optical path between the optical path changer and the photodetector 100 to focus the incident light so that it can be received by the photodetector 100 .
- the compatible optical pickup device further includes a diffraction element 250 disposed between the light source 50 and the optical path changer to diffract the light emitted from the light source 50 .
- the diffraction element 250 is used to detect a DPP (differential push-pull) signal used for tracking when a DVD-RAM is reproduced, or to produce a tracking signal according to a three beams method when a CD is reproduced.
- the diffraction element 250 may be provided for the reproduction of each of a DVD-RAM and a CD. While not shown, it is understood that the diffraction element 250 may also be applied to the compatible optical pickup device shown in FIGS. 2 and 8.
- FIGS. 8 and 9 Since the remaining members of FIGS. 8 and 9 are the same as those described with reference to FIG. 2, the same reference numerals are used therefor and detailed descriptions thereof will be omitted.
- the compatible optical pickup device according to the present invention is not limited to the optical configuration as shown in FIGS. 2, 8 and 9 , and of course, a variety of modifications thereto are possible.
- the compatible optical pickup devices according to the embodiments of the present invention use a single light source 50 to emit light having a wavelength longer than 650 nm, and which is preferably, a wavelength between 680 nm through 780 nm, the system cost is lowered.
- the compatible optical pickup device includes an objective lens 70 designed to have an effective numeral aperture suitable for the first and second optical disks 40 a and 40 b in relation to the wavelength of the light emitted from the single light source 50 , a light spot having an FWHM equal to or less than 0.72 ⁇ m is formed with respect to the first optical disk 40 a , while a light spot having an FWHM greater than or equal to 0.8 ⁇ m is formed with respect to the second optical disk 40 b .
- the compatible optical pickup device can compatibly reproduce/record the first and second optical disks 40 a and 40 b having different thicknesses.
- a light source emits light having a wavelength greater than or equal to 750 nm is adopted as the light source 50 , recording/reproduction of a presently commercialized CD-R and DVD-R is possible.
- properties of the objective lens 70 according to the present invention which is designed to compatibly reproduce/record the first and second optical disks 40 a and 40 b with respect to a 780 nm wavelength and a conventional objective lens for a DVD with respect to a 650 nm wavelength (not shown) (hereinafter referred to as an objective lens for 650 nm) are compared with each other.
- Table 1 shows data values of the objective lens 70 of the present invention with respect to the first optical disk 40 a (i.e., an example of design values for a DVD).
- the working distance is a distance between the surface of the objective lens 70 facing the optical disk 40 and the surface of the optical disk 40 on which light is incident.
- the second optical disk 40 b i.e., a CD
- the working distance is reduced by 0.3 mm.
- the aberration properties in the case of a DVD are shown in FIGS. 10A through 11B.
- a value of 0.04 ⁇ indicated by dotted lines of FIGS. 10A through 11B is allowable optical aberration (OPDrms) with respect to a DVD in the optical disk system.
- the objective lens for 650 nm has a numerical aperture of 0.61 while the objective lens 70 of the present invention is designed to have a numerical aperture of 0.73. That is, the objective lens 70 of the present invention has a numerical aperture greater than that of the conventional objective lens for 650 nm. While the objective lens for 650 nm has a working distance of 1.8 mm, the objective lens 70 of the present invention has a working distance of 1.3 mm. Of course, when a CD is to be reproduced/recorded, the working distance is reduced by 0.3 mm as shown in FIGS. 2 , and 6 A through 9 .
- the effective diameter of the objective lens for 650 nm is 4.03 mm and the focal distance is 3.3 mm, while the objective lens 70 of the present invention has an effective diameter of 4.09 mm and a focal distance of 2.8 mm. While a maximum angle of the curved surface of the objective lens for 650 nm is 51°, the objective lens 70 of the present invention has a maximum angle of the curved surface of 55°. The above maximum angle is a value which can be manufactured.
- FIGS. 10A and 10B show the aberration properties according to incident beam fields of the objective lens 70 of the present invention and the objective lens for 650 nm designed according to the data of Table 1.
- the objective lens for 650 nm shows an OPDrms of 0.06 ⁇ with respect to a field height of 1.0°
- the objective lens 70 of the present invention shows an OPDrms of 0.033 ⁇ , exhibiting a superior field aberration as compared to that of the objective lens for 650 nm.
- the field aberration is generated when the light emitted from the light source 50 is incident on the objective lens 70 at an inclined angle.
- an objective lens 70 preferably has a field aberration equal to or less than 0.04 ⁇ which is an allowable optical aberration value, with respect to a field height of 1° considering allowances in the assembly of the optical pickup device.
- FIGS. 11A and 11B show the aberration properties according to the inclination of the optical disk 40 of the objective lens 70 of the present invention and the objective lens for 650 nm designed according to the data of Table 1, with respect to the tilt of the optical disk 40 in which an allowable tilt angle of an optical disk system is 0.35°.
- the objective lens 70 of the present invention has an OPDrms of 0.041 ⁇ which is similar to the OPDrms of 0.038 ⁇ exhibited by the objective lens for 650 nm.
- the objective lens 70 of the present invention when a DVD is reproduced/recorded, the objective lens 70 of the present invention designed with respect to a wavelength of 780 nm exhibits an aberration property which is similar to or superior to the conventional objective lens for a DVD designed with respect to a wavelength of 650 nm. Also, the objective lens 70 of the present invention has a numerical aperture greater than that of the conventional objective lens for a DVD. Accordingly, even when light having a wavelength greater than 650 nm is used, a light spot having a small size suitable for reproducing/recording a DVD can be formed.
- a compatible optical pickup device using a single light source for a wavelength longer than 650 nm can compatibly reproduce/record not only the second optical disk 40 b of a CD family, but also the first optical disk 40 a of a DVD family.
- the size of a light spot is proportional to ⁇ /NA ( ⁇ is a wavelength and NA is the numerical aperture of the objective lens 70 ).
- ⁇ is a wavelength
- NA is the numerical aperture of the objective lens 70 .
- FIG. 12 shows values of reproduction signals according to the depth of a pit when a DVD is reproduced by a compatible optical pickup device according to an embodiment of the present invention.
- the reproduction signals are obtained with respect to values of reproduction signals detected when a DVD having a pit having a depth of ⁇ /6 is reproduced by a conventional DVD dedicated apparatus.
- the 780 nm light source 50 and the objective lens 70 having numerical aperture greater than that of the conventional objective lens for 650 nm with respect to a DVD are used, in the case in which the depth of a pit of a DVD is ⁇ /6, since about 90% of the amplitude of the signal can be detected as compared to the signal by the conventional DVD dedicated apparatus, a DVD can be reproduced.
- the compatible optical pickup device includes an inexpensive single light source to emit light having a wavelength longer than 650 nm and an objective lens, designed in relation to the wavelength of the light emitted from the light source to form a light spot having an FWHM equal to or less than 0.72 ⁇ m with respect to an optical disk of a DVD family and a light spot having an FWHM greater than or equal to 0.8 ⁇ m with respect to an optical disk of a CD family, it has both an inexpensive and simple structure and can compatibly reproduce/record an optical disk of both the CD and DVD family.
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Head (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Abstract
Description
- This application claims the benefit of Korean Application Nos. 2000-39091 and 2001-39757, filed respectively on Jul. 8, 2000 and Jul. 4, 2001, in the Korean Industrial Property Office, the disclosures of which are incorporated herein by reference.
- 1. Field of the Invention
- The present invention relates to a compatible optical pickup device which can compatibly read/write optical disks of the CD family or DVD family, and more particularly, to a compatible optical pickup device using a single light source to emit light having a wavelength longer than 650 nm.
- 2. Description of the Related Art
- A typical optical pickup device reproduces and records information on and/or from a recording medium in a non-contact manner. An optical pickup device capable of performing reproducing/recording of optical disks of the DVD family having a thickness of 0.6 mm (hereinafter referred to as “DVD”) uses an objective lens having a numerical aperture of 0.6 and a light source to emit light having a 650 nm wavelength. Here, the optical pickup device for DVD should be compatible with optical disks of a CD family which is 1.2 mm thick (hereinafter referred to as “CD”).
- In consideration of the above matter, optical pickup devices which can compatibly reproduce/record optical disks in different formats have been suggested. A conventional optical pickup which can compatibly reproduce/record a CD and a DVD is shown in FIG. 1 and has the structure using two
light sources - Referring to FIG. 1, a
first light source 1 emits light having 635 or 650 nm to reproduce/record aDVD 10 a, which is relatively thin. Asecond light source 3 emits light having a 780 nm wavelength to reproduce/record aCD 10 b, which is relatively thick. A grating 5 diffracts and splits light output from thesecond light source 3 into the 0th order and the ±1st order rays to detect a tracking error signal by a three-beam method during reproducing/recording of theCD 10 b. The light emitted from thefirst light source 1 passes through afirst beam splitter 7 and is reflected by a second beam splitter 9 so as to proceed toward theDVD 10 a. The light emitted from thesecond light source 3 is sequentially reflected by the first andsecond beam splitters 7 and 9 and proceeds toward theCD 10 b. Acollimating lens 11 converts the divergent light output from the first andsecond light sources objective lens 15 focuses incident light output from the first andsecond light sources first light source 1 is focused on the relativelythin DVD 10 a while the light emitted from thesecond light source 3 is focused on the relativelythick CD 10 b. - The light reflected by an
optical disk 10 is incident on the second beam splitter via theobjective lens 15. Most of the light passes through the second beam splitter 9 and is received by aphotodetector 19 after passing through a sendinglens 17 to focus the incident light reflected by theoptical disk 10. - Since the conventional compatible optical pickup device having the above structure includes two
light sources optical disks 10 of both theCD 10 b family and theDVD 10 a family can be reproduced/recorded. - However, since the conventional compatible optical pickup device uses two separate light sources, a cost of manufacturing is high and the structure thereof is complicated, and further, assembly and optical arrangement is difficult. Further, the
light source 1 for a 635 nm or 650 nm wavelength which can emit recording power for DVD-R and/or DVD-RAM is expensive, which increases the entire cost of a compatible optical pickup device. - To solve the above and other problems, it is an object of the present invention to provide an inexpensive compatible optical pickup device using a single light source to emit light having a wavelength longer than 650 nm so that an optical disk of the CD family and the DVD family can be compatibly reproduced/recorded.
- Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
- Accordingly, to achieve the above and other objects, there is provided a compatible optical pickup device according to an embodiment of the present invention comprises a single light source to emit a light having a wavelength longer than 650 nm, an objective lens having a near axis area, a ring type annular lens area, and a far axis area with respect to an apex to focus the light emitted from the light source to form light spots suitable for a first optical disk which is relatively thin and a second optical disk which is relatively thick, so as to form a light spot having an FWHM (full width at half maximum) of 0.72 μm or less with respect to the first optical disk and a light spot having an FWHM greater than or equal to 0.8 μm with respect to the second optical disk, an optical path changer arranged on the optical path between the light source and the objective lens to change a path of incident light, and a photodetector to receive light reflected by the optical disk passed through the objective lens and the optical path changer and to detect an information signal and/or error signal.
- According to another embodiment of the present invention, a compatible optical pickup device comprises a single light source to emit a light having a wavelength longer than 650 nm, an objective lens having a near axis area, a ring type annular lens area, and a far axis area with respect to an apex to focus light emitted from the light source to form light spots suitable for a first optical disk which is relatively thin and a second optical disk which is relatively thick, and having an effective numerical aperture greater than or equal to 0.63 with respect to the first optical disk and an effective numerical aperture less than or equal to 0.53 with respect to the second optical disk, an optical path changer arranged on the optical path between the light source and the objective lens to change a path of the incident light, and a photodetector to receive the light reflected by the optical disk and passed through the objective lens and the optical path changer and to detect an information signal and/or error signal.
- According to an aspect of the present invention, the first optical disk is an optical disk of a DVD family and the second optical disk is an optical disk of a CD family.
- According to another aspect of the present invention, the light source emits light having a wavelength between 680-780 nm.
- According to yet another aspect of the present invention, the annular lens area of the objective lens is optimized to the second optical disk so that, when the first optical disk is to be reproduced/recorded, a light spot of light passing through the near axis area and the far axis area is focused on the information recording surface of the first optical disk, while, when the second optical disk is to be reproduced/recorded, a light spot of light passing through the near axis area and the annular lens area is focused on the information recording surface of the second optical disk.
- According to still another aspect of the present invention, the optical path changer comprises a polarization hologram element to diffract incident light to the 0th order ray, or +1st order and/or −1st order rays according to a linear polarization component thereof, and a wave plate to change a polarization of the incident light.
- According to a further aspect of the present invention, the optical path changer comprises a beam splitter arranged between the light source and the objective lens to transmit and/or reflect incident light.
- According to a yet further aspect of the present invention, the beam splitter is provided to transmit or reflect incident light according to the polarization of the incident light, and a wave plate to change the polarization of the incident light is provided between the beam splitter and the objective lens.
- The above other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments thereof with reference to the attached drawings in which:
- FIG. 1 schematically shows the optical arrangement of a conventional compatible optical pickup device;
- FIG. 2 schematically shows the optical arrangement of a compatible optical pickup device using a single light source according to an embodiment of the present invention;
- FIG. 3 is a graph schematically showing reflectance rates as a function of wavelength before and after recording of cyanine based CD-R and phthalo based CD-R, which are currently known;
- FIG. 4 is a graph schematically showing reflectance rates as a function of wavelength before and after recording of azo based DVD-R and cyanine based DVD-R, which are currently known;
- FIG. 5 is a plan view of the objective lens according to an embodiment of the present invention of FIG. 2;
- FIGS. 6A and 6B and7A and 7B show the objective lens according to embodiments of the present invention for use in the compatible optical pickup of FIG. 2;
- FIG. 8 schematically shows the optical arrangement of a compatible optical pickup device using a single light source according to another embodiment of the present invention;
- FIG. 9 schematically shows the optical arrangement of a compatible optical pickup device using a single light source according to yet another embodiment of the present invention;
- FIGS. 10A and 10B are graphs indicating an aberration characteristic according to the field of an incident beam between the objective lens according to an embodiment of the present invention and the conventional 650 nm objective lens;
- FIGS. 11A and 11B are graphs indicating an aberration characteristic according to the tilt of an optical disk between the objective lens according to an embodiment of the present invention and the conventional 650 nm objective lens; and
- FIG. 12 is a graph showing a reproduction signal value according to the depth of a pit when a DVD is reproduced by the compatible optical pickup device according to an embodiment of the present invention.
- Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.
- Referring to FIG. 2, a compatible optical pickup device according to an embodiment of the present invention includes a
single light source 50 to emit a light having a wavelength longer than 650 nm, anobjective lens 70 mounted and driven on an actuator (not shown) to focus and track so as to control the formation of a light spot suitable for each of the first and secondoptical disks light source 50, anoptical path changer 60 disposed on an optical path between thelight source 50 and theobjective lens 70 to change a proceeding path of the incident light, and aphotodetector 100 to receive the light reflected by anoptical disk 40. Here, the firstoptical disk 40 a is an optical disk of the DVD family which is relatively thin and the secondoptical disk 40 b is an optical disk of the CD family which is relatively thick. - As shown, the
light source 50 is a semiconductor laser that emits a light of a high optical power (i.e., an edge emitting laser or a vertical cavity surface emitting laser) to be used not only for reproducing information signals, but also for recording information signals. Thelight source 50 emits light having a wavelength longer than 650 nm, for example, a wavelength between 660 nm through 790 nm. As shown, thelight source 50 emits light having a wavelength between 680 nm through 780 nm. - Here, with respect to a recording optical power for a DVD-R and/or DVD-RAM, the unit cost of production of a semiconductor laser for a wavelength longer than 650 nm is much lower than that of a semiconductor laser for a 650 nm wavelength. Thus, according to the present invention, the unit cost of production of the
light source 50 can be drastically reduced. For example, when a 680 nm semiconductor laser is used as thelight source 50, since the unit cost of production of the 680 nm semiconductor laser is much lower than a 650 nm semiconductor laser used as a general light source for a DVD, the unit cost of production of the compatible optical pickup device according to the present invention can be drastically reduced. - When the
light source 50 is a semiconductor laser that emits a light having a wavelength over 750 nm, the cost of the compatible optical pickup device according to the present invention can be lowered, and simultaneously a CD-R which is currently commercialized can be compatibly reproduced/recorded. Specifically, since the currently commercialized CD-R has an organic pigment film recording layer having a large absorptivity with respect to light having a wavelength less than 750 nm, in order to reproduce/record the CD-R, a light source that emits a light having a wavelength equal to or greater than 750 nm is needed to prevent the destruction of recorded data due to a difference in sensitivity. Of course, it is understood that if the CD-R is manufactured to have a small absorptivity with respect to the light having a wavelength equal to or less than 750 nm, the compatible optical pickup device according to the present invention can compatibly reproduce/record CD-Rs regardless of a wavelength range of the usedlight source 50. - Since a CD-R has a recording layer which is a organic pigment film having a large absorption rate with respect to light having a wavelength less than or equal to 750 nm, to use the CD-R, a light source is needed that emits light having a wavelength greater than or equal to 750 nm to prevent damage to recorded data due to the difference of sensitivity. As such, if the
light source 50 is a semiconductor laser that emits light having a wavelength less than or equal to 770 nm (preferably 760±10 nm), the compatible optical pickup device according to the present invention can be manufactured at a low cost and simultaneously be compatible with currently commercialized CD-Rs and DVD-Rs regardless of the type of organic pigment used therein. - As shown in FIGS. 3 and 4, the currently commercialized CD-Rs and DVD-Rs are different in the absorption rate depending on the type of organic pigment film used therein. That is, as shown in FIG. 3, a cyanine-based CD-R and a phthalo-based CD-R, which are currently commercialized, are optimized to exhibit a large difference in the reflection rate before and after recording with respect to a wavelength of 780 nm. The difference in the reflection rate before and after recording according to the wavelength is characteristically different with respect to the organic pigment used therefor. In particular, the CD-R has a great absorption rate with respect to light having a wavelength less than or equal to 750 nm. Thus, to use the CD-R, there is a need to use a light source that emits light having a wavelength greater than or equal to 750 nm to prevent damage to recorded data due to the difference in sensitivity.
- As shown in FIG. 4, an azo-based DVD-R and a cyanine-based DVD-R, which are currently commercialized, are optimized to exhibit a large difference in the reflection rate before and after recording with respect to a wavelength of 650 nm. As with the CD-R, the difference in the reflection rate before and after recording according to the wavelength is characteristically different with respect to the organic pigment used therefor. In particular, in the azo-based DVD-R, the reflection rate is reversed in a wavelength area longer than about 770 nm. That is, the reflection rate before recording either becomes less than the reflection rate after recording, or the difference in the reflection rate before and after recording is approximately 0. Thus, as shown in FIGS. 3 and 4, considering the feature of the reflection rate before and after recording of a DVD-R and a CD-R according to the type of organic pigment and the feature of the absorption rate of a CD-R, when the
light source 50 emits light having a wavelength which is longer than 750 nm and shorter than 770 nm (e.g., a wavelength of 760 nm), a CD-R and a DVD-R can be compatibly used regardless of the type of organic pigment in use. - However, when a CD-R is manufactured to have a less absorption rate with respect to light having a wavelength less than or equal to 750 nm, the compatible optical pickup device according to the present invention can compatibly use a CD-R regardless of the wavelength range of the
light source 50 used. Also, for example, when an azo-based DVD-R is manufactured such that a reflection rate thereof is not reversed with respect to light having a wavelength greater than or equal to 770 nm, or the difference in the reflection rate before and after recording is great, the compatible optical pickup device according to the present invention can compatibly use a DVD-R regardless of the wavelength range of the light source in use. - When a semiconductor laser is provided as the
light source 50, thelight source 50 emits linearly polarized light approximately in one direction. Thus, theoptical path changer 60 comprises a holographic beam splitter having apolarization hologram element 61 to diffract incident light into a 0th order ray, or a +1st order and/or the −1st order rays according to a linear polarization component, and awave plate 63 to convert the polarization of the incident light. In this case, most of the light emitted from thelight source 50 proceeds toward theoptical disk 40 while most of the light reflected by theoptical disk 40 is received by thephotodetector 100, so that the efficiency in use of the light is high. - The
polarization hologram element 61 is preferably arranged to diffract the light output from thelight source 50 and linearly polarize the light in one direction into the 0th order ray. Preferably, thewave plate 63 is a quarter wave plate with respect to the wavelength of the light emitted from thelight source 50 and is arranged to convert the linearly polarized light output from thelight source 50 to a circularly polarized light. Thus, the light output from thelight source 50 and linearly polarized light in one direction is diffracted into the 0th order ray by thepolarization hologram element 61, converted to one circularly polarized light while passing through thewave plate 63, and focused on the information recording surface of theoptical disk 40 by theobjective lens 70. The focused light is reflected by the information recording surface of theoptical disk 40 and converted to another circularly polarized light. The another circularly polarized light is converted to light linearly polarized in the other direction while passing through thewave plate 63 and diffracted into the +1st order and/or −1st order rays by thepolarization hologram element 61, and proceeds toward thephotodetector 100. Thephotodetector 100 receives light reflected by theoptical disk 40 and having passed through theobjective lens 70 and theholographic beam splitter 60, and detects an information signal and/or an error signal. Thephotodetector 100 includes a plurality of sectional plates (not shown), each of the sectional plates independently performing photoelectric conversion to detect the information signal and/or the error signal. - When the
optical path changer 60 is the holographic beam splitter, since thephotodetector 100 can be installed on a base 101 where thelight source 50 is installed, thephotodetector 100 and thelight source 50 can be modularized. Here, theholographic beam splitter 60 has a holographic device (not shown) by which most of the light output from thelight source 50 is diffracted into the 0th order ray, and most of the light reflected from theoptical disk 40 is diffracted into the +1st order ray and/or −1st order ray to be received by thephotodetector 100. - The
collimating lens 65 forms an indefinite optical system by changing the divergent light output from thelight source 50 to a parallel light. The collimatinglens 65 is preferably arranged between theoptical path changer 60 and theobjective lens 70. In this case, the collimatinglens 65 converts the divergent light output from thelight source 50 to a parallel light and, simultaneously, the light reflected by theoptical disk 40 and incident thereon to a focused light to proceed toward thephotodetector 100. - As shown in FIG. 5, the
objective lens 70 has anear axis area 71, a ring typeannular lens area 73, and afar axis area 75 with respect to an apex. Here, the apex is a point at the intersection of the central axis of theobjective lens 70 and the surface of theobjective lens 70. Theannular lens area 73 is an area on which light of an intermediary area between thenear axis area 71 and thefar axis area 75 is incident, which is formed to be an oval ring or circular ring type on the surface of theobjective lens 70 facing thelight source 50 or therecording medium 40. - According to another embodiment of the present invention, the
annular lens area 73 is formed to be aspherical as shown in FIGS. 6A and 6B and is optimized with respect to the relatively thick secondoptical disk 40 b. If theannular lens area 71 has an aspherical shape optimized with respect to the secondoptical disk 40 b, when the relatively thin firstoptical disk 40 a is to be reproduced/recorded, the light emitted from thelight source 50 passes through thenear axis area 71 and thefar axis area 75 and is thus focused on the information recording surface of the firstoptical disk 40 a. The light which passes through theannular lens area 73 between thenear axis area 71 and thefar axis area 75 is so spread that this light cannot reproduce/record information to/from the information recording surface of the firstoptical disk 40 a. - When the second
optical disk 40 b is used, of the light emitted from thelight source 50, the light passing through thenear axis area 71 and theannular lens area 73 is focused on the information recording surface of the secondoptical disk 40 b as a light spot, while the light passing through thefar axis area 75 is so spread so that it cannot be used to reproduce information from the information recording surface of the secondoptical disk 40 b. - Alternatively, the
annular lens area 73, as shown in FIGS. 7A and 7B, can be formed to shield or scatter incident light. In this case, when the firstoptical disk 40 a is used, of the light emitted from thelight source 50, the light passing through thenear axis area 71 and thefar axis area 75 is focused on the information recording surface of the firstoptical disk 40 a as a light spot, while the light passing through theannular lens area 73 is shielded or scattered so that it cannot be focused on the information recording surface of the firstoptical disk 40 b. Also, when the secondoptical disk 40 b is used, of the light emitted from thelight source 50, the light passing through thenear axis area 71 is focused on the information recording surface of the secondoptical disk 40 b as a light spot. In contrast, the light passing thefar axis area 75 is not focused on the information recording surface of the secondoptical disk 40 b with an intensity suitable for reproducing and/or recording, while the light passing through theannular lens area 73 is shielded or scattered so that it is not focused on the information recording surface of the secondoptical disk 40 b. - The
objective lens 70 having the structure according to the present invention is provided to focus the light output from thelight source 50 so that a light spot suitable for each of the first and secondoptical disks objective lens 70 according to the present invention preferably forms a light spot having an FWHM (full with at half maximum) equal to or less than 0.72 μm (a width which is equal to or less than 1.2 μm at 1/e2) with respect to the firstoptical disk 40 a, and a light spot having an FWHM equal to or greater than 0.8 μm (a width which is equal to or greater than 1.3 μm at 1/e2) with respect to the secondoptical disk 40 b. - In order to form a light spot having the above size, the
objective lens 70 has a numerical aperture related to the wavelength of the light emitted from thelight source 50. That is, when thelight source 50 emits light having a wavelength between 680-780 nm, theobjective lens 70 has an effective numerical aperture greater than or equal to 0.63 with respect to the firstoptical disk 40 a, and an effective numerical aperture less than or equal to 0.53 with respect to the secondoptical disk 40 b. When thelight source 50 emits light having a 780 nm wavelength, theobjective lens 70 preferably has an effective numerical aperture equal to or greater than 0.7 with respect to the firstoptical disk 40 a, and an effective numerical aperture less than or equal to 0.53 with respect to the secondoptical disk 40 b. - For example, when the
light source 50 emits light having a wavelength of 680 nm, 720 nm, 760 nm, or 780 nm, theobjective lens 70 has an effective numerical aperture of about 0.63, 0.66, 0.7, or 0.72 with respect to the firstoptical disk 40 a. Also, when thelight source 50 emits light having a wavelength between 750-780 nm, theobjective lens 70 preferably has an effective numerical aperture of 0.7 or more with respect to a DVD and 0.53 or less with respect to a CD. For example, when thelight source 50 emits light having a wavelength of 760±10 nm, theobjective lens 70 preferably has an effective numerical aperture of 0.7 with respect to a DVD and 0.53 with respect to a CD. - Here, FIG. 2 shows a case in which the
objective lens 70 having theannular lens area 73 having an aspherical shape described with reference to FIG. 6A is used. In particular, in FIG. 2, theobjective lens 70 is schematically illustrated to show the focus of the light according to the incident areas. Also, in FIGS. 2 and 6A through 7B, the light incident surface of the secondoptical disk 40 b is disposed closer to theobjective lens 70 than the light incident surface of the firstoptical disk 40 a. This is to show a difference in a distance between theobjective lens 70 and the light incident surface of the firstoptical disk 40 a and a distance between theobjective lens 70 and the light incident surface of the secondoptical disk 40 b (i.e., a working distance difference). In an actual system, the light incident surfaces of the first and second optical disks are located at the same position, and when the secondoptical disk 40 b is used, theobjective lens 70 is driven by an actuator to be moved closer to the secondoptical disk 40 b than in the firstoptical disk 40 a to be suitable for the working distance. - According to additional embodiments of the present invention as shown in FIGS. 8 and 9, the compatible optical pickup device includes a beam splitter type optical path changer. As shown in the embodiment of the present invention in FIG. 8, the optical path changer is a
polarizing beam splitter 161 disposed between thelight source 50 and theobjective lens 70 to transmit or reflect the incident light according to its polarization, and awave plate 163 disposed between thepolarizing beam splitter 161 and theobjective lens 70 to convert the polarization of an incident light. As shown in the embodiment of the present invention in FIG. 9, the optical path changer is abeam splitter 260 disposed between thelight source 50 and theobjective lens 70 to transmit and reflect the incident light in a predetermined ratio. When the above beam splitter type optical path changer is provided, asensing lens 167 is disposed on the optical path between the optical path changer and thephotodetector 100 to focus the incident light so that it can be received by thephotodetector 100. - In addition, the compatible optical pickup device according to the embodiment of the present invention shown in FIG. 9 further includes a
diffraction element 250 disposed between thelight source 50 and the optical path changer to diffract the light emitted from thelight source 50. Thediffraction element 250 is used to detect a DPP (differential push-pull) signal used for tracking when a DVD-RAM is reproduced, or to produce a tracking signal according to a three beams method when a CD is reproduced. Thediffraction element 250 may be provided for the reproduction of each of a DVD-RAM and a CD. While not shown, it is understood that thediffraction element 250 may also be applied to the compatible optical pickup device shown in FIGS. 2 and 8. - Since the remaining members of FIGS. 8 and 9 are the same as those described with reference to FIG. 2, the same reference numerals are used therefor and detailed descriptions thereof will be omitted.
- The compatible optical pickup device according to the present invention is not limited to the optical configuration as shown in FIGS. 2, 8 and9, and of course, a variety of modifications thereto are possible.
- Since the compatible optical pickup devices according to the embodiments of the present invention use a single
light source 50 to emit light having a wavelength longer than 650 nm, and which is preferably, a wavelength between 680 nm through 780 nm, the system cost is lowered. Also, since the compatible optical pickup device according to the present invention includes anobjective lens 70 designed to have an effective numeral aperture suitable for the first and secondoptical disks light source 50, a light spot having an FWHM equal to or less than 0.72 μm is formed with respect to the firstoptical disk 40 a, while a light spot having an FWHM greater than or equal to 0.8 μm is formed with respect to the secondoptical disk 40 b. Thus, the compatible optical pickup device according to the present invention can compatibly reproduce/record the first and secondoptical disks light source 50, recording/reproduction of a presently commercialized CD-R and DVD-R is possible. - With reference to Table 1 and FIGS. 10A, 10B,11A and 11B, properties of the
objective lens 70 according to the present invention which is designed to compatibly reproduce/record the first and secondoptical disks - Table 1 shows data values of the
objective lens 70 of the present invention with respect to the firstoptical disk 40 a (i.e., an example of design values for a DVD). The working distance is a distance between the surface of theobjective lens 70 facing theoptical disk 40 and the surface of theoptical disk 40 on which light is incident. When the secondoptical disk 40 b (i.e., a CD) is reproduced/recorded, the working distance is reduced by 0.3 mm. The aberration properties in the case of a DVD are shown in FIGS. 10A through 11B. A value of 0.04 λ indicated by dotted lines of FIGS. 10A through 11B is allowable optical aberration (OPDrms) with respect to a DVD in the optical disk system.TABLE 1 Objective Lens Objective (present Lens invention) (conventional) Remarks NA 0.73 0.61 Working Distance 1.3 1.8 Reduced by 0.3 mm (mm) in the case of a CD Effective Diameter 4.09 4.03 (mm) Focal Distance (mm) 2.8 3.3 Maximum Angle of 55° 51° Possible to Curved Surface of manufacture Lens OPDrms at Field 0.033λ 0.060λ Height of 1.0° OPDrms at Optical 0.041λ 0.038λ Allowable Optical Disk Tilt of 0.35° Disk Tilt: 0.35° - Referring to Table 1, the objective lens for 650 nm has a numerical aperture of 0.61 while the
objective lens 70 of the present invention is designed to have a numerical aperture of 0.73. That is, theobjective lens 70 of the present invention has a numerical aperture greater than that of the conventional objective lens for 650 nm. While the objective lens for 650 nm has a working distance of 1.8 mm, theobjective lens 70 of the present invention has a working distance of 1.3 mm. Of course, when a CD is to be reproduced/recorded, the working distance is reduced by 0.3 mm as shown in FIGS. 2, and 6A through 9. The effective diameter of the objective lens for 650 nm is 4.03 mm and the focal distance is 3.3 mm, while theobjective lens 70 of the present invention has an effective diameter of 4.09 mm and a focal distance of 2.8 mm. While a maximum angle of the curved surface of the objective lens for 650 nm is 51°, theobjective lens 70 of the present invention has a maximum angle of the curved surface of 55°. The above maximum angle is a value which can be manufactured. - FIGS. 10A and 10B show the aberration properties according to incident beam fields of the
objective lens 70 of the present invention and the objective lens for 650 nm designed according to the data of Table 1. As shown, the objective lens for 650 nm shows an OPDrms of 0.06 λ with respect to a field height of 1.0°, while theobjective lens 70 of the present invention shows an OPDrms of 0.033 λ, exhibiting a superior field aberration as compared to that of the objective lens for 650 nm. Here, the field aberration is generated when the light emitted from thelight source 50 is incident on theobjective lens 70 at an inclined angle. Thus, anobjective lens 70 preferably has a field aberration equal to or less than 0.04 λ which is an allowable optical aberration value, with respect to a field height of 1° considering allowances in the assembly of the optical pickup device. - FIGS. 11A and 11B show the aberration properties according to the inclination of the
optical disk 40 of theobjective lens 70 of the present invention and the objective lens for 650 nm designed according to the data of Table 1, with respect to the tilt of theoptical disk 40 in which an allowable tilt angle of an optical disk system is 0.35°. As shown, theobjective lens 70 of the present invention has an OPDrms of 0.041 λ which is similar to the OPDrms of 0.038 λ exhibited by the objective lens for 650 nm. - As can be seen from the above, when a DVD is reproduced/recorded, the
objective lens 70 of the present invention designed with respect to a wavelength of 780 nm exhibits an aberration property which is similar to or superior to the conventional objective lens for a DVD designed with respect to a wavelength of 650 nm. Also, theobjective lens 70 of the present invention has a numerical aperture greater than that of the conventional objective lens for a DVD. Accordingly, even when light having a wavelength greater than 650 nm is used, a light spot having a small size suitable for reproducing/recording a DVD can be formed. Thus, in a compatible optical pickup device using a single light source for a wavelength longer than 650 nm can compatibly reproduce/record not only the secondoptical disk 40 b of a CD family, but also the firstoptical disk 40 a of a DVD family. - Here, the size of a light spot is proportional to λ/NA (λ is a wavelength and NA is the numerical aperture of the objective lens70). Thus, since the
objective lens 70 of the present invention has numerical aperture greater than a typical objective lens for a DVD, even when light having a wavelength longer than 650 nm is used, a small light spot needed to reproduce/record the firstoptical disk 40 a of a DVD family can be formed. - FIG. 12 shows values of reproduction signals according to the depth of a pit when a DVD is reproduced by a compatible optical pickup device according to an embodiment of the present invention. In FIG. 12, the reproduction signals are obtained with respect to values of reproduction signals detected when a DVD having a pit having a depth of λ/6 is reproduced by a conventional DVD dedicated apparatus. As shown in FIG. 12, when the 780 nm
light source 50 and theobjective lens 70 having numerical aperture greater than that of the conventional objective lens for 650 nm with respect to a DVD are used, in the case in which the depth of a pit of a DVD is λ/6, since about 90% of the amplitude of the signal can be detected as compared to the signal by the conventional DVD dedicated apparatus, a DVD can be reproduced. - As described above, since the compatible optical pickup device according to the present invention includes an inexpensive single light source to emit light having a wavelength longer than 650 nm and an objective lens, designed in relation to the wavelength of the light emitted from the light source to form a light spot having an FWHM equal to or less than 0.72 μm with respect to an optical disk of a DVD family and a light spot having an FWHM greater than or equal to 0.8 μm with respect to an optical disk of a CD family, it has both an inexpensive and simple structure and can compatibly reproduce/record an optical disk of both the CD and DVD family.
- Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
Claims (20)
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
KR2000-39091 | 2000-07-08 | ||
KR20000039091 | 2000-07-08 | ||
KR2001-39757 | 2001-07-04 | ||
KR1020010039757A KR100750104B1 (en) | 2000-07-08 | 2001-07-04 | Compatible optical pickup apparatus adopting sigle light source |
Publications (2)
Publication Number | Publication Date |
---|---|
US20040090900A1 true US20040090900A1 (en) | 2004-05-13 |
US7116627B2 US7116627B2 (en) | 2006-10-03 |
Family
ID=26638198
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/899,501 Expired - Fee Related US7116627B2 (en) | 2000-07-08 | 2001-07-06 | Compatible optical pickup device using a single light source |
Country Status (2)
Country | Link |
---|---|
US (1) | US7116627B2 (en) |
JP (1) | JP2002092934A (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20050207328A1 (en) * | 2002-05-31 | 2005-09-22 | Matsushita Electric Industrial Co., Ltd. | Optical recording medium, optical information processor, and optical recording/reproducing method |
US20050243433A1 (en) * | 2002-12-03 | 2005-11-03 | Essilor International, A France Corporation | Polarization splitter, method of manufacturing same and ophthalmic lens incorporating projection inserts containing it |
US20060067204A1 (en) * | 2002-12-04 | 2006-03-30 | Koninklijke Philips Electronics N.V. | Objective lens and scanning device using such an objective lens |
US20060158989A1 (en) * | 2005-01-19 | 2006-07-20 | Samsung Electronics Co., Ltd. | Diffraction element and optical pick-up apparatus having the same |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN100407313C (en) * | 2003-04-25 | 2008-07-30 | 宾得株式会社 | Optical system of optical pick-up |
JP4568133B2 (en) * | 2004-03-30 | 2010-10-27 | 三洋電機株式会社 | Semiconductor laser device and optical device |
TWI383390B (en) * | 2004-04-22 | 2013-01-21 | Panasonic Corp | Light emitting device and information processing apparatus |
US7612725B2 (en) | 2007-06-21 | 2009-11-03 | Apple Inc. | Antennas for handheld electronic devices with conductive bezels |
JP2009151878A (en) * | 2007-12-21 | 2009-07-09 | Sanyo Electric Co Ltd | Optical pickup apparatus |
US8106836B2 (en) | 2008-04-11 | 2012-01-31 | Apple Inc. | Hybrid antennas for electronic devices |
Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5446565A (en) * | 1993-02-01 | 1995-08-29 | Matsushita Electric Industrial Co., Ltd. | Compound objective lens having two focal points |
US6043912A (en) * | 1997-03-28 | 2000-03-28 | Samsung Electronics Co., Ltd. | Optical pickup compatible with a digital versatile disk and a recordable compact disk using a holographic ring lens |
US6088322A (en) * | 1998-05-07 | 2000-07-11 | Broome; Barry G. | Single objective lens for use with CD or DVD optical disks |
US6091691A (en) * | 1997-02-13 | 2000-07-18 | Samsung Electronics Co., Ltd. | Optical pickup having an objective lens compatible with a plurality of optical disk formats |
US6188594B1 (en) * | 1999-06-09 | 2001-02-13 | Neomagic Corp. | Reduced-pitch 6-transistor NMOS content-addressable-memory cell |
US6259668B1 (en) * | 1996-02-14 | 2001-07-10 | Samsung Electronics Co., Ltd. | Recording/reproducing apparatus having an optical pickup device to read from and record information to disks of different thicknesses |
US6480344B1 (en) * | 1999-11-22 | 2002-11-12 | Asahi Kogaku Kogyo Kabushiki Kaisha | Objective lens for optical pick-up |
US6898168B2 (en) * | 2000-05-12 | 2005-05-24 | Konica Corporation | Optical pick-up apparatus |
Family Cites Families (15)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
KR0166233B1 (en) | 1995-11-27 | 1999-03-20 | 배순훈 | Subminiature dual focus optical pick-up device |
JPH1069675A (en) | 1995-12-19 | 1998-03-10 | Konica Corp | Optical pickup device, objective lens of optical pickup and optical disk device |
KR100238266B1 (en) | 1996-02-14 | 2000-02-01 | 윤종용 | Optical device |
KR0176595B1 (en) | 1996-04-30 | 1999-04-15 | 김광호 | Objective lens device and optic pick-up device using objective lens device |
JPH1021638A (en) | 1996-06-28 | 1998-01-23 | Victor Co Of Japan Ltd | Optical information recording and reproducing apparatus |
EP1103958A3 (en) | 1996-10-23 | 2004-10-06 | Konica Corporation | Method for recording/reproducing optical information recording medium, optical pickup apparatus |
JP4038843B2 (en) | 1996-10-23 | 2008-01-30 | コニカミノルタホールディングス株式会社 | Optical information recording medium recording / reproducing method, optical pickup device, condensing optical system, objective lens, and objective lens design method |
JP3613745B2 (en) | 1996-11-12 | 2005-01-26 | コニカミノルタホールディングス株式会社 | Optical pickup device and objective lens |
KR100209916B1 (en) | 1997-02-13 | 1999-07-15 | 윤종용 | Optical pickup for various disc specification |
DE69840116D1 (en) | 1997-03-13 | 2008-11-27 | Hitachi Maxell | Optical lens and optical pickup |
JP3775011B2 (en) | 1997-09-09 | 2006-05-17 | コニカミノルタホールディングス株式会社 | Optical pickup device |
KR100514323B1 (en) | 1997-12-05 | 2005-12-08 | 삼성전자주식회사 | Optical pickup with objective lens compatible with multiple optical discs |
JPH11339306A (en) | 1998-05-29 | 1999-12-10 | Seiko Epson Corp | Optical head and optical recording device |
WO2000000964A1 (en) | 1998-06-26 | 2000-01-06 | Asahi Kogaku Kogyo Kabushiki Kaisha | Objective lens for optical pick-up |
JP4517407B2 (en) | 1998-07-14 | 2010-08-04 | コニカミノルタホールディングス株式会社 | Optical pickup device for recording / reproducing optical information recording medium |
-
2001
- 2001-07-06 US US09/899,501 patent/US7116627B2/en not_active Expired - Fee Related
- 2001-07-06 JP JP2001206834A patent/JP2002092934A/en active Pending
Patent Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5446565A (en) * | 1993-02-01 | 1995-08-29 | Matsushita Electric Industrial Co., Ltd. | Compound objective lens having two focal points |
US6259668B1 (en) * | 1996-02-14 | 2001-07-10 | Samsung Electronics Co., Ltd. | Recording/reproducing apparatus having an optical pickup device to read from and record information to disks of different thicknesses |
US6091691A (en) * | 1997-02-13 | 2000-07-18 | Samsung Electronics Co., Ltd. | Optical pickup having an objective lens compatible with a plurality of optical disk formats |
US6198714B1 (en) * | 1997-02-13 | 2001-03-06 | Samsung Electronics Co., Ltd. | Optical pickup having an objective lens compatible with a plurality of optical disk formats |
US6043912A (en) * | 1997-03-28 | 2000-03-28 | Samsung Electronics Co., Ltd. | Optical pickup compatible with a digital versatile disk and a recordable compact disk using a holographic ring lens |
US6088322A (en) * | 1998-05-07 | 2000-07-11 | Broome; Barry G. | Single objective lens for use with CD or DVD optical disks |
US6188594B1 (en) * | 1999-06-09 | 2001-02-13 | Neomagic Corp. | Reduced-pitch 6-transistor NMOS content-addressable-memory cell |
US6480344B1 (en) * | 1999-11-22 | 2002-11-12 | Asahi Kogaku Kogyo Kabushiki Kaisha | Objective lens for optical pick-up |
US6898168B2 (en) * | 2000-05-12 | 2005-05-24 | Konica Corporation | Optical pick-up apparatus |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20050207328A1 (en) * | 2002-05-31 | 2005-09-22 | Matsushita Electric Industrial Co., Ltd. | Optical recording medium, optical information processor, and optical recording/reproducing method |
US7656777B2 (en) * | 2002-05-31 | 2010-02-02 | Panasonic Corporation | Optical recording medium, optical information processor, and optical recording/reproducing method |
US20050243433A1 (en) * | 2002-12-03 | 2005-11-03 | Essilor International, A France Corporation | Polarization splitter, method of manufacturing same and ophthalmic lens incorporating projection inserts containing it |
US7163291B2 (en) * | 2002-12-03 | 2007-01-16 | Essilor International (Compagnie Generale D'optique) | Polarization splitter, method of manufacturing same and ophthalmic lens incorporating projection inserts containing it |
US20060067204A1 (en) * | 2002-12-04 | 2006-03-30 | Koninklijke Philips Electronics N.V. | Objective lens and scanning device using such an objective lens |
US20060158989A1 (en) * | 2005-01-19 | 2006-07-20 | Samsung Electronics Co., Ltd. | Diffraction element and optical pick-up apparatus having the same |
US7643395B2 (en) * | 2005-01-19 | 2010-01-05 | Samsung Electronics Co., Ltd. | Diffraction element and optical pick-up apparatus having the same |
Also Published As
Publication number | Publication date |
---|---|
US7116627B2 (en) | 2006-10-03 |
JP2002092934A (en) | 2002-03-29 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
KR100195137B1 (en) | Compatible optical pickup | |
US6552974B1 (en) | Compatible optical pickup | |
RU2155389C2 (en) | Design of optical detector, lens, and optical interface device | |
US7116627B2 (en) | Compatible optical pickup device using a single light source | |
US6404709B1 (en) | Optical pickup device | |
EP1892705A2 (en) | Optical pick-up | |
EP1047052A2 (en) | Compatible optical pickup for DVD-RAM reproduction | |
US6400666B1 (en) | Optical pickup device | |
JP2004521437A (en) | Optical scanning device | |
US6400671B2 (en) | Optical head device | |
KR100750104B1 (en) | Compatible optical pickup apparatus adopting sigle light source | |
US7079471B1 (en) | Optical pickup using two laser beam sources of different wavelengths for an optical disk drive and a converter to optimize a light beam reflected off an optical disc for detection based on reflected light beam wavelength | |
KR19990080322A (en) | Compatible Optical Pickup Device | |
KR100565036B1 (en) | Compatible optical pickup apparatus | |
KR100281880B1 (en) | Compatible optical pickup | |
KR100370205B1 (en) | Compatible optical pick-up | |
JP2818405B2 (en) | Optical pickup device equipped with a wave plate | |
KR100682689B1 (en) | Optical pick up having a multiple light emitting devices | |
KR100265740B1 (en) | Compatible optical pickup apparatus | |
KR100265734B1 (en) | Compatible optical pickup apparatus | |
KR100234306B1 (en) | An optical pickup | |
KR100600587B1 (en) | Optical pick-up | |
JP2000215500A (en) | Optical pick-up device and object lens | |
JPH10247338A (en) | Optical pickup device | |
JP4732289B2 (en) | Optical pickup device |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: SAMSUNG ELECTRONICS CO., LTD., KOREA, REPUBLIC OF Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:YOO, JANG-HOON;JUNG, SEUNG-TAE;LEE, HO-CHEOL;AND OTHERS;REEL/FRAME:012262/0324 Effective date: 20010813 |
|
FPAY | Fee payment |
Year of fee payment: 4 |
|
FEPP | Fee payment procedure |
Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY Free format text: PAYER NUMBER DE-ASSIGNED (ORIGINAL EVENT CODE: RMPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY |
|
FPAY | Fee payment |
Year of fee payment: 8 |
|
FEPP | Fee payment procedure |
Free format text: MAINTENANCE FEE REMINDER MAILED (ORIGINAL EVENT CODE: REM.) |
|
LAPS | Lapse for failure to pay maintenance fees |
Free format text: PATENT EXPIRED FOR FAILURE TO PAY MAINTENANCE FEES (ORIGINAL EVENT CODE: EXP.); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY |
|
STCH | Information on status: patent discontinuation |
Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362 |
|
FP | Lapsed due to failure to pay maintenance fee |
Effective date: 20181003 |